Thursday, April 25, 2013

Both valueOf and parseInt methods
are used to convert String to Integer in Java, but there are subtle difference
between them. If you look at code of valueOf() method, you
will find that internally it calls parseInt() method to convert String to Integer, but
it also maintains a pool of Integers from -128 to 127 and if requested integer
is in pool, it returns object from pool. Which means two integer objects
returned using valueOf() method can be same by equality operator. This
caching ofImmutable object, does help in
reducing garbage and help garbage collector. Another difference between parseInt() and valueOf() method is
there return type. valueOf() of java.lang.Integer returns an
Integer object, while parseInt() method returns an int primitive.
Though, after introducing Autoboxing in Java 1.5, this
doesn't count as a difference, but it's worth knowing.

ParseInt vs valueOf in Java

If you look code of parseInt() and valueOf() method
from java.lang.Integer class, you will find that actual job of converting
String to integer is done by parseInt() method, valueOf() just
provide caching of frequently used Integer objects, Here is code snippet from valueOf() method
which makes things clear:

This method first calls parseInt() method, in
order to convert String to primitive int,
and then creates Integer object from that value. You can see it internally
maintains an Integer cache. If primitive int is within range of cache, it
returns Integer object from pool, otherwise it create a new object.

There is always confusion, whether to use parseInt() or valueOf() for
converting String to primitive int and java.lang.Integer, I would
suggest use parseInt() if you need primitive int and use valueOf() if you
need java.lang.Integer objects. Since immutable objects are safe to be pooled
and reusing them only reduces load on garbage collector, it's better
to use valueOf() if you need Integer object.

@Anonymous, You are right, good understanding of basic API e.g. java.lang, java.util are extremely important for effective programming in Java. By the way good catch, parseInt() is used for converting String to primitive int :)